Did you know there were over 300 tweets with the hashtag #cats yesterday around 2pm?
Did you know there were about 50 tweets with the hashtag #bespoke around 6am today?
Did you know that #custom was tweeted yesterday afternoon?
How do I know this?
The website
http://www.hashtags.org trends Twitter hashtags.
I recommend trying a few words related to your artwork. Perhaps "custom", "artwork", "pets", etc.
Find the ones that both relate to your product AND have trending traffic. Then start to liberally sprinkle them throughout your tweets. Such as:
"Love your pet Airdale? Why not get a custom-made work of art? Affordable, beautiful, OOAK. #pet #airdale #custom #artwork"
This is not THE answer, but it is at least ONE of them.
Hope this helps.